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Lecture 22 - Virulence, Symptoms, and Portals of Exit
Virulence Virulence is the degree to of pathogenicity within a group or species of parasites. Definitions Invasiveness How much it spreads throughout the body. Toxigenicity How much toxins a pathogen generates. Exaltation An increase in virulence caused by a more susceptible host, mutations, plasmids, or lysogenic conversion. Attenuation A decrease in virulence by growing organism in an environment less favorable to their growth, such as lab media, heated media, or media with inhibitory chemicals. Acute Short duration, rapid onset of a disease. For example, a common cold, the flu, Strep sore throat, Hepatitis A are all acute, and do not cause as many long terms Chronic Slow onset, long duration and very damaging. Examples include Hepatits B, Hepatitis C, TB, and AIDS Systemic Spreads throughout the entire body, through the blood stream and into organs, eventually affecting all tissues if not treated. Lyme disease and syphilis are systemic. Local Confined to a single area, a local infection has not spread. Examples of local infection can include a pimple, a tetanus will stay at the puncture wound. Pulmonary TB stays in the lungs. Focal The spread of a local infection to other parts of the body. This happens when you push a pimple down (it can go systemic), tetanus (it releases toxins), TB (can turn secondary, extra-pulmonary) Septicemia (Blood Poisoning) Septicemia refers to the presence of pathogens or toxins in blood. Bacteremia, toxemia (diphtheria affects the heart, tetanus the brain), fungemia, and viremia are specific terms for specific types of organisms. Systemic Inflammatory Response Syndrome (SIRS) Characterized by change in temperature (fever or hypothermia) and a drastic change in white blood cells (either increase or decrease) Sepsis A whole body inflammatory response to a systematic bacterial infection. It is characterized SIRS plus documented infection by microbial culture. Severe sepsis involves organ failure, and septic shock involves refractory hypotension (low blood pressure that does not respond to treatment) and decreased blood flow to extremities, also known as decreased peripheral perfusion. Pyemia Septicemia caused by a systematic bacterial infection (often staph/strep) that triggers pus-forming by neutrophils. Sapremia When a saprophyte grows on the dead tissue of a live host. Gangrene, for instance, grows on body parts that have died due to poor blood circulation. Organisms can also grow on a retained placenta. Invasiveness Invasiveness measures how well an organism can spread in a host. Any enzyme that helps a pathogen spread to spread is referred to as an aggressin. Sometimes aggressins are Hyaluronidase Hyaluronidase breaks down hyaluronic acid, which is a cementing agent in humans that holds cells together, so if a bacteria can break down hyaluronic acid, it can also move between tissues, increasing its invasiveness. Clostridium perfringens and Strep pyogenes both produce this aggressin. Collagenase Collagenase breaks down collagen, a protein found in connective tissue, tendons. Anaerobes such as Clostridium perfringens tend to produce collagenase because connective tissue often don't have much innervation, and therefore little oxygen flow. Lecithinase Lecithinase breaks down lecithin, which is a phospholipid that has choline as an R group. An organism with lecithinase can break down phospholipids and destroy cell membranes. This is particularly effective in destroying red blood cells, which have no regenerative potential. Therefore, lecithinase is considered a toxin, more specifically a hemolysin, that causes anemia, anoxia (loss of oxygen), and hopoxia (decrease in oxygen). Clostridium perfringens makes lecithinase, but it can be treated by exposing it to oxygen since it is an anaerobe. This can be done by opening up the infection and airing it out. Streptolysin A hemolysin produced by Streptococcus pyogenes. This hemolysin causes strep sore throat, and makes Streptococcus pyogenes show beta hemolysis. This toxin makes the organism more pathogenic by causing anemia and anoxia. Leucocidin Leucocidins are especially dangerous because they break down any white blood cell that phagocytizes bacteria (neutrophils). Staphylococci/Streptococcus produce leucocidin, and will defend themselves against the hosts' immune system, resulting in pus and sores. Kinases Kinases include staphylokinase and streptokinase, which break down the fibrin that humans use to produce a clot. Highly pathogenic and hard to get rid of. Toxigenicity Endotoxins Endotoxins are a non-specific toxin released by the outer (second) membrane of Gram-negative bacteria when it is broken down. Endotoxins can cause fevers with as few as 100ng or 10M cells. With more cells, the colony of bacteria can cause Gram-negative shock, hypotension (low blood-pressure), organ failure, and death. Even if a sample is sterile, it can still contain these pyrogenic endotoxins, which are heat labile but can be cleaned with filters. Immuno-compromised patients like diabetics are especially vulnerable. Treating a Gram-negative infection with cidal antibiotics can cause a sudden release of endotoxins, causing decreased respiration and previously mentioned symptoms. Exotoxins Exotoxins are any toxins that are released by bacteria that are also not endotoxins. Clostridium tetani Tetanospasmin, a neurotoxin, causes tetanus, which causes lockjaw and paralysis of affected muscles. If it reaches the diagram, it prevents the host from breathing. Streptococcus pyogenes Streptococcus pyogenes produces erythrogenic toxin, which is a superantigen that causes a hypersensitive response where the skin peels off known as scarlet fever. Staphylococcus aureus Staph produces enterotoxins, which causes vomitting and diarrhea. Escherichia coli E. coli produces enterotoxin, and since E. coli is Gram-negative, also releases endotoxin when its second membrane is broken down. Lethal Doses 1 mg of endotoxin is enough to kill 10 mice 1mg of Botulinum type A toxin (botox) is enough to kill 200 million mice. If you isolated one cup, there would be enough to kill all humans. Signs, Symptoms, Syndromes Signs are objective, quantitative evidence of disease such as fever, swelling, and paralysis. Symptoms are more subjective, qualitative evidence of disease such as malaise (nauseousness) and pain Syndromes '''are group of signs and symptoms that will define an illness like the cold or the flu. Portals of Exit Methods by which a pathogen can exit a host to transmit to another host. Usually a lot of pathogens are spread before symptoms show (healthy carriers) '''Feces Commonly spreads E. coli, shigella, polio, hepatitis A, salmonella, typhoid fever ***** Urine Commonly spreads gonorrhea (drip, causes excessive mucus), which transfers to urethra (sex) and pharynx (bjs), and typhoid fever. Sputum Sputum (spit) refers to the pathogens that spread through microareosols from the nose. Spreads the cold, flu, TB, pertussis, diphtheria, and rabies, but NOT AIDS, which only have 1virus/mL. Secretions Bodily secretions are a common way to transfer STDs like gonorrhea and syphilis, and other diseases such as chicken pox and MRSA Blood Human blood can contain AIDS, and Hepatitis B/C, and malaria when in an insect vector.